The present invention relates generally to a high-power pulsing circuit and more particularly to a repetitive pulse inductive energy storage and transfer circuit for an electromagnetic launcher.
Electromagnetic launchers are generating considerable interest because their projectile launch velocities are not limited to the sonic velocity of an expanding gas, as in conventional guns. In the railgun, the simplest and most successful type of electromagnetic launcher, a projectile sliding between two parallel rails acts as a sliding switch or electrical short between them. By passing a large current down one rail, through the projectile (or a conducting sabot or plasma behind it), and back along the other rail, a large magnetic field is built up behind the projectile, accelerating it to a high velocity by the force of the current times the magnetic field. Projectile velocities over 10 kilometers per second can be obtained by this method.
Electromagnetic launchers of the railgun type have the problem that the launch process is inefficient. Even under the ideal conditions of constant-current drive and no dissipative losses, only one-half of the energy extracted from the power source is transferred to the projectile. The remainder goes into building up the magnetic field behind the projectile or, equivalently, into energizing the railgun inductance. If the energy stored in the inductance of the rails is not recovered after each launch operation, then it will be dissipated (in the rail resistance and in a muzzle blowout arc). Under these conditions, therefore, the best operational efficiency (projectile energy/power supply energy delivered) that repetitive railguns can achieve is 50 percent. Of course, dissipative losses in switches, the rail resistance, or a plasma arc behind the projectile only serve to reduce the operational efficiency below this limit.
One possibility for utilizing the inductively-stored rail energy is the breech crowbar circuit which uses a crowbar switch at the breech of the railgun to crowbar or short circuit the driving power supply when the projectile has reached some fraction of its launch velocity. Thereafter, the projectile is further accelerated by the expansion of the magnetic field trapped in the railgun behind the projectile. Unfortunately, the barrel length has to be doubled to convert one-half of the trapped magnetic energy to projectile kinetic energy and quadrupled to convert 75% of the trapped energy (assuming no dissipative losses). While technically feasible, the breech crowbar scheme results in a very large increase in railgun barrel length and never recovers all of the trapped energy.
High pulse power repetitive pulse inductive storage circuits have been disclosed in applications Ser. No. 617,653 and Ser. No. 617,658 both filed on June 5, 1984, and issued as U.S. Pat. No. 4,642,476 on Feb. 10, 1987, and U.S. Pat. No. 4,613,765 on Sept. 23, 1986, respectively. These applications illustrate some advantages of repetitive pulse indicative storage circuits and describe the type of switches that can be used therewith. These applications are incorporated by reference.
Therefore, it is an object of the present invention to provide a high-power energy transfer circuit with the capability to recover energy stored in the inductance of the load.
It is another object of the present invention to provide a repetitive energy transfer and recovery circuit.
It is another object of the present invention to provide an efficient energy transfer and recovery circuit using survivable switches.
It is still another object of the present invention to provide an energy transfer circuit for railgun electromagnetic launchers which can recover the energy from the load inductance without increasing the barrel length over that required for normal acceleration.